side=10;
delta=0.1;
/*
*
*不知道为什么会报错。
*
intersection(){
    translate([0,0,delta])
        cylinder(h=side,r1=side/2,r2=side/2,$fn=100);
    polyhedron([[5,-5,0],[-5,-5,0],[0,-5,10],[5,5,0],[-5,5,0],[0,5,10]],[[0,1,2],[5,4,3],[0,2,5,3],[1,4,5,2],[0,1,4,3]]);
}
*/

intersection(){
    //translate([0,0,delta])
        cylinder(h=side,r1=side/2,r2=side/2,$fn=500);
    rotate([90,0,0])
    translate([0,0,-side])
        linear_extrude(height = 20)
                polygon([[side/2, 0],[-side/2, 0],[0,side]], center = true);
}